Acquired immunodeficiency syndrome (“AIDS”) has been described as the first great pandemic of the second half of the twentieth century. Gallo, Sci. Am., 256:39 (1987). Human immunodeficiency virus (“HIV”) is the etiological agent of AIDS. A complete sequencing of the HIV genome indicates that it contains the same overall gag-pol-env organization as other retroviruses. Ratner et al., “Complete Nucleotide Sequence of the AIDS virus, HTLV-III,” Nature 313:277-84 (1985). HIV invades a host cell and uses the host cell's machinery to replicate itself.
HIV can be cultured from most tissues and body fluids of infected individuals. Saliva represents a significant exception. In an early report, HIV-1 was isolated from only one of 71 saliva samples of HIV+donors (Ho et al., “Infrequency of Isolation of HTLV-III Virus from Saliva in AIDS,” New Engl. J. Med. 313:1606 (1985)). Recent work confirmed the paucity of infectious virus in saliva (Groopman et al., “HTLV-III in Saliva of People with AIDS-Related Complex and Healthy Homosexual Men at Risk for AIDS,” Science, 226:447-449 (1994)), with a mean viral load in 25 samples of 162 genome equivalent/ml, at the limits of detection by reverse transcription-polymerase chain reaction (“RT-PCR”) (Liuzzi et al., “Analysis of HIV-1 Load in Blood, Semen and Saliva: Evidence for Different Viral Compartments in a Cross-Sectional and Longitudinal Study,” AIDS, 10:F10-F56 (1996)). Clinical support for the limited transmissibility of HIV by saliva includes: lack of infection following contamination of open wounds with saliva from HIV+individuals (CDC, “Update: Universal Precautions for Prevention of Transmission of Human Immunodeficiency Virus, Hepatitis B Virus, and Other Blood-Borne Pathogens in Healthcare Settings,” Morbid. Mortal. Wkly. Rep., 37:377-388 (1988)); low occupational risk for HIV infection among dentists in practices with large numbers of patients at risk for HIV infection (Klein et al., “Low Occupational Risk of Human Immunodeficiency Virus Infection Among Dental Professionals,” New Engl. J. Med., 318:86-90 (1988)); and the inability to infect adult chimpanzees by direct application of HIV to intact oral mucosa (Fultz, “Components of Saliva Inactivate Human Immunodeficiency Virus,” Lancet, ii: 1215 (1986)).
Such retarded transmission is not a general characteristic of viruses which can be shed orally. The annual attack rate for hepatitis B virus among unvaccinated dentists is 2.6% (Remis et al., “Hepatitis B Infection in a Day School for Mentally Retarded Students: Transmission from Students to Staff,” Am. J. Public Health, 77:1183-1186 (1987)), human T cell lymphotrophic virus type I is found in saliva (Achiron et al., “Detection of Proviralpuman T-Cell Lymphotropic Virus Type I DNA in Mouthwash Samples of HAM/TSP Patients and HTLV-I Carriers,” Arch. Virol., 141:147-153 (1996)), and the type D retrovirus etiologic in a simian immune-deficiency syndrome can be readily isolated from macaque saliva and spread by this fluid (Lercke et al., “Inapparent Carrier of Simian Acquired Immune Deficiency Type D Retrovirus and Disease Transmission with Saliva,” J. Natl. Cancer Inst., 77:489-495 (1986)). The ability of saliva to suppress HIV-1 also is relatively specific. It does not alter the infectivity of Herpes simplex virus (Malamud et al., “Human Submandibular Saliva Aggregates HIV,” AIDS Res. Hum. Retroviruses, 9:633-637 (1993)), and both cytomegalovirus and Epstein-Barr virus are readily shed in oral secretions of HIV seronegative (Fox et al., “Saliva Inhibits HIV-1 Infectivity,” J. Am. Dent. Assoc., 116:635-637 (1988)) and seropositive persons (Alsip et al., “Increased Epstein-Barr Virus DNA in Oropharygeal Secretions from Patients with AIDS, AIDS-Related Complex, or Asymptomatic Human Immunodeficiency Virus Infections,” J. Infect. Dis., 157:1072-1076 (1988); Scholes et al., “Oral Shedding of CMV and HSV in Relation to HIV Disease,” IXth Intl. Conf. AIDS, Berlin, June 6 -11:Abst. PO-B18-1801-(1993)).
In contrast, other body fluids from HIV+individuals contain HIV in relatively high titers, including tears (CDC, “Recommendations for Preventing Possible Transmission of Human T-Lymphotropic Virus Type III/Lymphadenopathy-Associated Virus from Tears,” Morbid. Mortal. Wkly. Rep., 34:533-534 (1986)), genital secretions (Mostad et al., “Shedding of HIV in the Genital Tract,” AIDS, 10:1305-1315 (1996)), feces (Yolken et al., “Persistent Diarrhea and Fecal Shedding of Retroviral Nucleic Acids in Children Infected with Human Immunodeficiency Virus,” J. Infect. Dis., 164:61-66 (1991)), and breast milk (VandePerre et al., “Infective and Anti-Infective Properties of Breast Milk from HIV-1 Infected Women,” Lancet, 341:914-918 (1993)). Genital secretions, feces, and breast milk have all been implicated in HIV transmission.
Particulate and filterable oral secretions capable of inhibiting HIV infection represent potential explanations for the paucity of HIV in saliva. Reports from several different groups imply that two processes are involved (Fultz, “Components of Saliva Inactivate Human Immunodeficiency Virus,” Lancet, ii: 1215 (1986); Malamud et al., “Human Submandibular Saliva Aggregates HIV,” AIDS Res. Hum. Retroviruses, 9:633-637 (1993); Fox et al., “Saliva Inhibits HIV-1 Infectivity,” J. Am. Dent. Assoc., 116:635-637 (1988); Fox et al., “Salivary Inhibition of HIV-1 Infectivity: Functional Properties and Distribution in Men, Women and Children,” J. Am. Dent. Assoc., 118:709-711 (1989); Archibald et al., “In Vitro Inhibition of HIV-1 Infectivity by Human Salivas,” AIDS Res. Hum. Retroviruses, 6:1425-1432 (1990); McNeely et al., “Secretory Leukocyte Protease Inhibitor: A Human Saliva Protein Exhibiting Anti-Human Immunodeficiency Virus 1 Activity In Vitro,” J. Clin. Invest., 96:456-464 (1995); Malamud et al., “HIV in the Oral Cavity: Virus, Viral Inhibitory Activity, and Antibodies: A Review,” Crit. Rev. Oral. Biol. Med., 4:461-466 (1993); Amory et al., “The Large Molecular Weight Glycoprotein MGI, a Component of Human Saliva, Inhibits HIV-1 Infectivity,” Clin. Res., 40:51A (1992); Yeh et al., “Further Studies of Salivary Inhibition of HIV-I Infectivity,” J. Acquired Immune Defic. Svndr., 5:898-903(1992); Bergey et al., “Interaction of HIV-1 and Human Salivary Mucins,” J. Acquired Immune Defic. Svndr., 7:995-1002 (1994); Phillips et al., “Low Level of Cell-Free Virus Detected at High Frequency in Saliva from HIV-1 Infected Individuals,” AIDS, 8:1011-1012 (1994)). Some studies found that whole saliva and submandibular secretions, but not parotid fluid, could sequester HIV virions (Malamud et al., “Human Submandibular Saliva Aggregates HIV,” AIDS Res. Hum. Retroviruses, 9:633-637 (1993); Fox et al., “Saliva Inhibits HIV-1 Infectivity,” J. Am. Dent. Assoc., 116:635-637 (1988); Fox et al., “Salivary Inhibition of HIV-1 Infectivity: Functional Properties and Distribution in Men, Women and Children,” J. Am. Dent. Assoc., 118:709-711 (1989); Archibald et al., “In Vitro Inhibition of HIV-1 Infectivity by Human Salivas,” AIDS Res. Hum. Retroviruses, 6:1425-1432 (1990); Bergey et al., “Interaction of HIV-1 and Human Salivary Mucins,” J. Acquired Immune Defic. Svndr., 7:995-1002 (1994)), while others identified soluble inhibitory factors capable of direct inhibition in secretions from all salivary glands, but only at very high concentrations (Yeh et al., “Further Studies of Salivary Inhibition of HIV-1 Infectivity,” J. Acquired Immune Defic. Syndr., 5:898-903 (1992); Phillips et al., “Low Level of Cell-Free Virus Detected at High Frequency in Saliva from HIV-1 Infected Individuals,” AIDS, 8:1011-1012(1994)). Submandibular saliva contains sulfated polysaccharides of low (MG2) and high (MG1) molecular weights (Levine et al., “Structural Aspects of Salivary Glycoproteins,” J. Dent. Res., 66:436-441 (1987)), with the latter forming an anionic charge barrier to binding of the high affinity HIV receptor, CD4, to the HIV envelope glycoprotein gp120 (Amory et al., “The Large Molecular Weight Glycoprotein MGI, a Component of Human Saliva, Inhibits HIV-1 Infectivity,” Clin. Res., 40:51A (1992)). Secretory leukocyte protease inhibitor (SLPI), a 12 kDa protein found in whole saliva, has an effect independent of HIV binding to CD4 (McNeely et al., “Secretory Leukocyte Protease Inhibitor: A Human Saliva Protein Exhibiting Anti-Human Immunodeficiency Virus I Activity In Vitro,” J. Clin. Invest., 96:456-464 (1995)), albeit its significance in vivo has been questioned (Bu et al., “Secretory Leukocyte Protease Inhibitor (SLPI) does not Effectively Inhibit HIV-1 Replication,” 35th ICAAC, San Francisco, Calif., Sept. 17-20:Abst. 1142 (1995)). Fibronectin, a matrix adhesion molecule, binds directly to gp120, but was shown to inhibit infectivity only at high concentrations (Su et al., “Interaction of the Envelope Glycoprotein of Human Immunodeficiency Virus with Clq and Fibronectin Under Conditions Present in Saliva,” Mol. Immunol., 28:811-817 (1991)).
None of the above-cited references has positively identified the factor in saliva which is capable of inhibiting HIV infectivity. The present invention is directed to overcoming this and other deficiencies in the art.